Rapid changes in heat production rate by Ischadium demissum demissum (=Modiolus demissus demissus, Geukensia demissa), largely though not exclusively effected by opening and closing of shell valves, signify changing metabolic states, physical activity level, and body processes with time and experimental condition. It is theorized that the relative rates of anaerobic metabolism and oxygen uptake, as influenced by temperature, and the presence or absence of unfavorable external stimuli all interact, in feedback mode, to regulate the opening and closing of shell valves. Knowledge of the pattern of instantaneous changes in metabolic rates of organisms is essential in analysis of, and interpreting and comparing data on, average metabolic rates. Direct calorimetry should be particularly useful in understanding the evolutionary ecology of facultatively anaerobic organisms. 相似文献
On the extensive sedimentary tidal flats of the Wadden Sea, beds of the blue mussel Mytilus edulis represent the only major hard substratum and attachment surface for sessile organisms. On this substratum, the barnacle Semibalanus balanoides is the most frequent epibiont. In summer 1998, it occurred on over 90% of the large mussels (>45 mm shell length) and the dry weight of barnacles reached 65% of mussel dry weight. However, the extent of barnacle overgrowth is not constant and differs widely between years. Periwinkles (Littorina littorea) may reach densities >2000 m–2 on intertidal mussel beds. Field experiments were conducted to test the effect of periwinkle grazing on barnacle densities. An experimental reduction of grazing and bulldozing pressure by periwinkles resulted in increased recruitment of barnacles, while barnacle numbers decreased with increasing snail density. The highest numbers of barnacles survived in the absence of L. littorea. However, a lack of periwinkle grazing activity also facilitated settlement of ephemeral algae which settled later in the year. Field experiments showed that the growth rate of barnacles decreased in the presence of these ephemeral algae. Thus, L. littorea may reduce initial barnacle settlement, but later may indirectly increase barnacle growth rate by reducing ephemeral algae. It is suggested that periwinkle density may be a key factor in the population dynamics of S. balanoides on intertidal mussel beds in the Wadden Sea. 相似文献
An effective system for in vitro regeneration of adventitious shoots from callus for the transformation or mutation of gerbera was developed. Callus was produced
from petioles of the youngest 3–4 leaves detached from auxillary shoots produced in vitro. Induction medium, on which leaves were incubated over 3 or 6 days, contained 2.3 μM thidiazuron and 0.53 μM α-naphthaleneacetic
acid. Explants were than transferred to one of three regeneration media with lower levels of growth regulators. Regeneration
was quantified over four (4-weeks each) passages at the time of explant transfer to fresh medium. Direct shoot regeneration
occurred during the first 4 weeks, and after these shoots were discarded a semi-compact organogenic callus was produced. Effectiveness
of shoot regeneration depended on four criteria: the cultivar (three cultivars were tested), the sequence of passage on regeneration
medium, the growth regulators in regeneration medium and the duration of the induction period. Regeneration potential from
calli of all cultivars increased from the first to the fourth passage. Duration of the incubation period on induction medium
(3 or 6 days) influenced regeneration to varying degrees, depending on the cultivar used and the regeneration medium contents.
There were no differences between two of the regeneration media – B, containing 2.2 μM 6-benzyladenine and 0.3 μM indole-3-acetic
acid and C, containing 4.4 μM 6-benzyladenine, 4.6 μM zeatin and 0.6 μM indole-3-acetic acid. Cultivar Mariola was the most
productive and regenerated more than seven shoots per callus in the fourth passage. Regeneration on medium B was further evaluated
on four additional gerbera cultivars.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
Multiple infection of individual hosts with several species or strains of maternally inherited endosymbionts is commonly observed in animals, especially insects. Here, we address theoretically the effect of co-infection on the optimal density of the endosymbionts in doubly infected hosts. Our analysis is based on the observation that a maternally inherited double infection is only stable if doubly infected females produce more doubly infected daughters than singly infected or uninfected females produce daughters. We consider both a general model and a model involving two endosymbionts inducing bidirectional cytoplasmic incompatibility (CI). We demonstrate that the optimal replication rate of endosymbionts in doubly infected hosts can be expected to be similar to or below the optimal replication rate in singly infected hosts. This is in contrast to some theoretical predictions for horizontally transmitted parasites and stems from the two strains of endosymbionts having coupled fitness. We discuss our results with respect to recent empirical results on endosymbiont densities, the evolution of CI-inducing bacteria and, more generally, the evolution of cooperation through direct fitness benefits. 相似文献
Summary Our study aimed to examine the applicability of a native plant restoration technique involving close grazing, blanket herbicide spraying and mob stocking (to trample the seed into the soil) for establishing New Zealand native tree and shrub species into exotic hill country pasture. This approach represents an alternative to the usual spaced-planting of seedlings in the context of an indigenous vegetation restoration programme. Field-collected seed of Cabbage Tree ( Cordyline australis ), Kahikatea ( Dacrycarpus dacrydioides ), Kanuka ( Kunzea ericoides ), Karamu ( Coprosma robusta ), Kohuhu ( Pittosporum tenuifolium ), Koromiko ( Hebe stricta ), and Manuka ( Leptospermum scoparium ) were germination tested in the laboratory, and broadcast sown in two field experiments in spring 2001 and autumn 2002. The spring-sown experiment tested the effect of mob stocking and the autumn-sown experiment tested the effect of mob stocking and sowing rate. Laboratory germination varied widely among species (0–88%). In the field, the two shrubs, Koromiko and Karamu, established densities of up to 5 and 1.2 plants/m2, respectively, after 2.5 years. Autumn emergence for these two species strongly related to sowing rate. Three tree species, Cabbage Tree, Kahikatea and Manuka, emerged in the field but did not survive beyond 6 months. Mob stocking was effective in spring but not autumn sowing, implicating soil moisture content as an important factor in germination success. The study demonstrated that the direct seeding technique was successful for two shrub species, highlighting the potential for development of a cost-effective native plant restoration approach. 相似文献
1. 1. The calorigenic responses of 60-h fasted (F) and control (C) guinea pigs to E. coli endotoxin (5 μg·kg−1 i.v.) injection were compared at Ta = 25°C.
2. 2. In contrast to fed (C) guinea pigs, the F group showed significantly lower calorigenic response.
3. 3. The brown adipose tissue (BAT) thermogenesis judge by the BAT temperature did not change significantly. Shivering activity was not different from that in the C group.
4. 4. The results conclude that fasting attenuates endotoxin-induced fever and this attenuation is due to suppression of nonshivering thermogenesis (NST) in guinea pigs.
5. 5. The results from direct calorimetry indicate that endotoxin injection evoked a prominent increase in heat production, while the changes in heat loss do not have an important role.
Author Keywords: E. coli endotoxin; starvatipn; brown adipose tissue; direct calorimetry; indirect calorimetry; shivering thermogenesis 相似文献